The present application relates to radio communications antennas and, more particularly, to a novel phase-variable antenna and to novel steerable arrays formed with a plurality of such antennas.
There is increasing interest in direct reception of radio-frequency signals, and particularly television signals, originating from geosynchronous satellites; such satellites are presently relaying many channels of program material to cable systems and network and public broadcasting stations. Recent reductions in the cost of low noise amplifiers and converters, for frequency-converting the microwave (C-band) signals to VHF or UHF channels receivable upon consumer television sets, opens the possibility for direct reception of satellite signals at the homes and apartment houses of the ultimate viewer. The antenna required for acceptable satellite television reception generally has an aperture of at least 10 feet, which relatively large aperture is required in order to capture a sufficient amount of signal energy to reduce "snow" and other deleterious picture artifacts, and to form a beam of sufficiently small width as to reduce the possibility of interference from adjacent satellites and terrestrial sources, such as microwave links and the like. Typically, a parabolic "dish" antenna is utilized, which must be fabricated of a RF reflective material (typically a metal or a metal-coated plastic) and requires an extremely sturdy mounting structure to maintain the large antenna precisely pointed at the satellite orbital position. In many locations, this large parabaloid and its mounting structure may meet with opposition for both aesthetic and zoning reasons. Further, unless the antenna and its mount are very sturdy, the large surface undergoes extreme wind loading and may pose a safety hazard.
It is therefore highly desirable to provide an antenna, and arrays thereof, which may be mounted flat against existing structural surfaces and which may be rendered unobtrusive, as by covering by plastic or the like material of a color and texture that matches the surface on which the array is mounted. By mounting the antenna array upon a building or other structure, the antenna is subject to no greater degree of wind damage than the structure itself. Phased arrays, comprising a two-dimensional field of antenna elements, are well known in the art. Typically, the beam heading of a prior art array must be adjusted: by either mechanically rotating the entire array; by adjusting a multiplicity of individual phase-shifters at a single frequency; or by adjusting the frequency of the entire array, for precise beam steering. It is therefore highly desirable to provide an array which may have the major lobe thereof steered by mechanical adjustment of each antenna in the array, and without requiring operational frequency variation or mechanical movement of the entire array.